The present disclosure relates to a radio frequency (RF) switching circuit and an electronic device.
Semiconductor integrated circuits (ICs) installed in communications systems include an RF switching circuit controlling a transmission path of an RF signal between an antenna, a transmission unit and a reception unit. Such an RF switching circuit is used in communications systems such as Bluetooth™, cellular personal communication service (PCS)/code division multiple access (CDMA)/wideband code division multiple access (WCDMA)/time division multiple access (TDMA)/global system/standard for mobile communications (GSM), and the like, as well as in local area networks (LAN).
In general, an RF switching circuit is used between a transmission unit and a reception unit in various communications systems using time-division multiplexing (TDM). Using an RF switching circuit, a transmission unit and a reception unit are alternately turned on and off, reducing overall power consumption of a system and interference between the transmission unit and the reception unit.
RF switching circuits are required to have low insertion loss, high isolation, high switching speeds, and high power handling capability, and also, to have low harmonic distortion, namely, high linearity, with respect to a large input signal.
As insertion loss increases, degradations of the sensitivity of a reception unit and transmission power loss of a transmission unit caused by a switch may be further reduced. Power handling capability guarantees maximum output power from a transmission unit. High isolation may minimize an influence on a reception unit in an OFF state when a transmission unit operates, and vice versa.
In particular, mobile communications systems are required to essentially have insertion loss and power handling capability.
In an existing wireless communications device, an RF switching circuit includes a plurality of RF ports respectively connected to a plurality of transmission units and reception units and a common port connected to an antenna.
The RF switching circuit controls a transmission path of an RF signal between the plurality of RF ports and the common port to allow one of the plurality of transmission units and reception units connected to the RF switching circuit to be selected and electrically connected to the antenna.
In order to change a transmission path of an RF signal between each of the RF ports and the common port, the existing RF switching circuit may include a switching circuit unit connected between each of the RF ports and the common port and a shunt circuit unit connected between each of the RF ports and a ground.
The switching circuit unit includes a transmission switching circuit unit (Tx SW) and a reception switching circuit unit (Rx SW), and each of the transmission switching circuit unit and the reception switching circuit unit may include a plurality of semiconductor switches.
The semiconductor switches, switching elements formed on a silicon-on-insulator (SOI) board, may be configured as metal oxide silicon field effect transistors (MOSFETs).
In the existing RF switching circuit, in preparation for applying a signal having a voltage higher than a breakdown voltage of a single transistor, the switching circuit unit may have a structure in which a plurality of transistors are stacked.
In the structure in which a plurality of transistors are stacked, a voltage higher than a rated voltage is dividedly applied to each of the plurality of transistors, and thus, a voltage applied to a single transistor is lowered, protecting the transistors from the high voltage.
In the existing RF switching circuit, a gate signal Vg lower or higher than a threshold voltage Vth of the transistors included in the transmission switching circuit unit and the reception switching circuit unit is provided to a gate of each of the transistors to control the transistors to be turned on or off. The gate signal Vg may be provided from a baseband chip set.
In order to secure isolation required between transmission units and reception units, the existing RF switching circuit may need a negative voltage generating unit providing a gate signal, as a negative voltage, for controlling the switching circuit unit for selecting a signal path to be turned off.
When such a negative voltage generating unit is additionally provided, complexity in design operation and costs increase as much.
Patent document 1 below relates to an RF switching circuit and a method of controlling an RF switching circuit. This document, however, does not disclose technical matters for generating a negative gate signal using a voltage of an RF signal in a common connection port to which an antenna is connected.